Cranial asymmetry (plagiocephaly) and deformations are common in the neonatal period. They may occur from various causes including premature closure of the cranial vault and/or skull base sutures (craniosynostosis), syndromal craniofacial dysostosis, intracranial volume disorders such as hydrocephalus, microcephaly or tumor, metabolic bone disorders such as rickets, and birth trauma such as depressed skull fractures. A subset of patients with plagiocephaly are recognized that do not exhibit pathology of the sutures and do not fall into any of the above categories. These patients are referred to as having plagiocephaly without synostosis (PWS), also known as "positional" or "gestational" plagiocephaly.
PWS is characterized by unilateral occipital flattening with contralateral occipital bulging or, put more simply, a flat spot at the back of the infant's head. As the deformation becomes more severe there is ipsilateral forehead protrusion, contralateral forehead flattening and endocranial skull base rotation with anterior displacement of the ipsilateral ear. The face becomes involved with anterior rotation of the cheek and mandible away from the side of involvement. If not corrected by one year of age, these deformities typically do not improve and remain into adulthood as proven by anthropometric measurements, though they are less noticeable secondary to camouflage by the hair.
The etiology of cranial asymmetry in PWS has been suggested to result from two possible mechanisms. One proposed mechanism is intrauterine constraint that develops from early descent of the fetal head into the pelvis, effectively placing uneven pressure on one area of the cranium within a confined space. This leads to constraint of one side of the occiput (back of the head) with a compensatory change to the contralateral skull. Another mechanism that can perpetuate the fetal constraint or even lead to the misshapen head is supine positioning of the infant. Once the occiput develops even a mildly flattened area, placing the infant on the back or supine position will perpetuate the deformity. The head will roll to the flattened area by the forces of gravity and, because motor control is lacking in the neonate, the deformity will remain or worsen. This effect is especially illustrated in infants with neuromuscular disorders and hypotonia where deformation of the cranium can be quite profound. This phenomena has been recognized for many years and recommendations for changing the infant's environment with relationship to the crib and placement within the sleeping area are well established.
An increased number of patients diagnosed with PWS after clinical and radiological evaluation resulted from a sudden increase of infant referrals from pediatricians and primary care specialists. This increase in referrals contemporaneously corresponded to the "Back-to-Sleep" campaign by the American Academy of Pediatrics (AAP), recommending that infants be placed in the supine (lying on the back) sleeping position in an effort to decrease the incidence of sudden infant death syndrome (SIDS). Similar findings in regard to referral patterns for patients with PWS and the timing of the AAP "Back-to-Sleep" campaign have been reported from numerous craniofacial centers around the country. For example, national statistics show a decrease in infant prone (lying on the stomach) sleeping position prevalence from 70% in 1992 to 24% in 1996. This decrease correlated with a 15-20% decrease in the incidence of SIDS.
SIDS is the leading cause of early infantile deaths in the United States. Approximately 6,000 infants die of this syndrome each year, an incidence of 1.2 deaths per 1,000 live births. Based on these data, the AAP Task Force on Infant Positioning and SIDS recommended that efforts be made to inform parents to place infants in the supine position, avoiding even a side position, to further lower the risk. The report recognized the increased incidence of flat spots on the occiput and recommended altering the baby's supine sleeping position by changing the orientation of the baby to the side or stomach during waking hours.
A causal relationship between the "Back to Sleep" campaign and PWS remains presumptive and is largely based on a temporal relationship. Although the issue of how the supine sleep position adversely affects the lambdoid suture remains unclear, it is reasonable to assume that the mechanism is related to a disturbance of sutural function and skull growth. Craniofacial anomalies secondary to suture pathology demonstrate the complex relationships that exists among skull, brain and facial development. Alterations in the normal growth pattern of one component can produce significant changes in others. In the case of synostosis or retardation of growth of the lambdoid suture, as is thought to occur in PWS, skull growth perpendicular to the dysfunctional suture is impeded and the occipital region on the side of the cranial suture becomes flattened. This observation dates back to 1851, when Virchow recognized that the shape of the skull deformations was predictable in cases of craniosynotosis depending on which suture was prematurely fused. He noted that not only was the skull growth retarded parallel to the abnormal suture, but that skull growth was enhanced in a perpendicular plane. Thus, in cases of lambdoid synostosis or untreated PWS, cranial growth is exaggerated in a frontal direction on the same side (ipsilateral frontal bossing) and in a posterior direction on the opposite side (contralateral occipital bossing). These changes are the result of the normal brain growth that exerts a force on the pliable cranium of the infant.
The clinical features of an infant with PWS are best appreciated when the child is examined from above, looking down on the vertex of the head. From this view, the skull has a trapezoid or parallelogram shape. Occipital bossing, contralateral occipital bulging, and ipsilateral frontal bossing are the most prominent features. This asymmetry may not be readily appreciated when the child is examined "face-on." The anterior compensatory cranial growth which results in frontal bossing also results in forward displacement of the petrous bone, which houses the ear and the temporomandibular joint. Infants with PWS frequently have forward and inferior displacement of the ear on the same side as the occipital flattening and deviation of the chin to the opposite side. An area of alopecia is frequently noted and marks the site of continuous head positioning.
The natural history of PWS is unknown. There is no evidence to suggest that single suture closure or dysfunction impedes brain growth and development. Infants with PWS have normal neurologic evaluations, no signs of raised intracranial pressure, and age appropriate developmental milestones. Further, the head circumference is typically within the normal range. Treatment is indicated, nevertheless, to alleviate the cosmetic and other effects on the growing child.
The treatment of PWS depends mainly on the infant's age and the degree of cranial distortion. The initial management of PWS is based on clinical rather than radiographic criteria, since skull x-rays are neither sufficiently sensitive nor specific to detect sutural abnormalities. The younger the infant and the less severe the skull asymmetry, the more likely the child will respond to conservative non-surgical treatments. Young infants (less than three months of age) who have occipital flattening are treated with repositioning only. Parents are instructed to keep the child off the flattened head region by using various repositioning maneuvers with a warning that the infant will initially resist these attempts. In the majority of cases, repositioning the infant on the opposite occipital region or in a lateral position is successful with some coaxing after several days and is usually all that is required. The head assumes a more normal symmetric shape with further cranial growth.
Older infants (more than three months of age) and those who have not responded to repositioning are placed in an individually tailored Cranial Augmentation Device or cranial molding helmet. The helmet is a custom fitted apparatus that is designed to apply continuous pressure to the cranium. This apparatus has proved to be very effective in allowing the growing brain to reshape the still-malleable cranium. It is applied continuously and removed only for bathing until the child is twelve months old. After twelve months of age or if the deformity is severe, molding helmets are of little value and surgical cranial recontouring is required.
Education of the parents regarding the importance of head repositioning should result in a reduction in positional PWS. Positional plagiocephaly is preventable by judicious and consistent manipulation of the infant's head. Such constant literal "hands-on" intervention is, however, impractical or impossible in many cases. Examples of such cases are during the many hours that an infant is asleep and/or while the infant is in the care of a less than vigilant caregiver. Thus, a cranial support apparatus to either supplement or replace constant hands-on intervention for the prevention or mitigation of PWS in an infant is needed.
Stated in another way, the supine or "on the back" sleeping position of infants, preferred to preclude the possibility of SIDS, may itself cause positional plagiocephaly or PWS, that is, malformation in the shape of the head of an infant. This malformation can be cosmetically distracting and functionally disruptive even into adulthood. It is thus desired to provide a method and apparatus which prevents PWS in infants and thus removes a potentially debilitating side effect from the well known measure of putting an infant to sleep on his or her back to prevent SIDS.